Internet Quality of Service

1. Internet Quality of Service

2. Quality of Service (QoS) • The best-effort model , in which the network tries to deliver data from source to destination but makes no promises about end-to-end delay, is not sufficient for real-time applications. • The primary goal of Quality of Service (QoS) is to support different levels of services by provide priorities including dedicated bandwidth, controlled jitter and latency (required by some real-time and interactive traffic), and improved loss characteristics.

3. Sampler, Microphone A D Buffer, D A converter Speaker Real-time Applications • Require “deliver on time” assurances • Example application (audio) • sample voice once every 125us • each sample has a playback time • packets experience variable delay in network • add constant factor to playback time: playback point

4. Playback Buffer Packet arrival Packet generation Playback Sequence number Buffer Network delay T ime

5. Application Requirements Time Sensitive no no no yes, 100’s msec yes, few secs yes, 100’s msec yes and no Application file transfer e-mail Web documents real-time audio/video stored audio/video interactive games financial apps Data loss no loss no loss loss-tolerant loss-tolerant loss-tolerant loss-tolerant no loss Bandwidth elastic elastic elastic audio: 5Kb-1Mb video:10Kb-5Mb same as above few Kbps up elastic

6. Taxonomy Applications Real time Elastic Asynchronous Interactive Interactive T olerant Intolerant bulk Adaptive Nonadaptive Rate-adaptive Nonadaptive Delay- Rate- adaptive adaptive

7. QoS Approaches • IPv4 Type of Service (TOS) • IPv6 Traffic class + Flow label • Integrated Services (Intserv) • Differentiated Services (Deffserv) • ATM service classes • CBR, VBR-rt, VBR-nrt, ABR, UBR

8. 1 2 3 4 5 6 7 8 Precedence TOS MBZ IPv4 • RFC1349 • Precedence: the importance or priority of the datagram • TOS: • 1000 -- minimize delay • 0100 -- maximize throughput • 0010 -- maximize reliability • 0001 -- minimize monetary cost • 0000 -- normal service • MBZ: Must Be Zero (Unused) • Suggested to be used as ECN field in RFC3168

9. Integrated Services • Intserv provides individualized quality-of-service guarantees to individual application sessions by per-flow resource reservation. • IETF intserv working group (concluded) • Resource ReSerVation Protocol (RSVP, RFC 2205) • Subnet Bandwidth Manager (SBM, RFC 2814)

10. Service Classes • Guaranteed service (RFC2212) • Provides firm bounds on the queueing delays that a packet will experience in a network element • Controlled-load service (RFC 2211) • provides the flow with a quality of service closely approximating the QoS that same flow would receive from an unloaded network element

11. Mechanisms • Traffic characterization • Tspec (RFC2210) • Rspec (RFC2215) • Admission control • Reservation protocol • RSVP • Packet processing • Weighted Fair Queuing (WFQ)

12. Flowspecs • Rspec: describes service requested from network • controlled-load: none • guaranteed: delay target • Tspec: describes flow’s traffic characteristics • average bandwidth + burstiness: token bucket filter • token rate r • bucket depth B • must have a token to send a byte • must have n tokens to send n bytes • start with no tokens • accumulate tokens at rate of r per second • can accumulate no more than B tokens

13. Token Bucket • If the service rate at a network element is R, then the queuing delay is bounded by b/R.

14. Admission Control • A router decides whether to admit a flow based on the R-spec and T-spec of the flow and currently available resources on the router.

15. Reservation Protocol • RSVP is employed in Intserv to setup path and reserve resources.

16. RSVP • Receiver-oriented reservation • Receiver heterogeneity • Designed to support multicast • Merge requirements in case of multicast

17. RSVP • Support multiple senders • Use soft state (refresh periodically) • Source transmits PATH messages every 30 seconds • Destination responds with RESV message • Separate from route establishment • QoS can change dynamically

18. Sender 1 PATH R Sender 2 R PATH RESV (merged) R RESV Receiver A R RESV R Receiver B RSVP

19. RSVP • RSVP does not specify how the network provides the reserved bandwidth to the data flows. • RSVP is not a routing protocol. • RSVP is a signaling protocol that allows host to establish and tear down reservations for data flows.

20. Packet Processing • Packet classification associates each packet with the appropriate reservation class. • IPv4: SA, DA, SP, DP, Protocol • IPv6: Flow label • Packet scheduling manages queues so that each packet receives the requested service. • Guaranteed: calculate end-to-end delay • Controlled load: assign the aggregate flow with a weight based on the amount of traffic admitted

21. WFQ • WFQ provides different amount of service among queues according to their weights.

22. Challenges • Scalability • Per-flow states • Overhead • Signaling messages • Refresh messages • Packet processing • Security • RSVP deny of service

23. Differentiated Services • Diffserv provides scalable and flexible service differentiation to handle different classes of traffic in different ways within the Internet. • IETF diffserv working group • DS field (RFC2474, 2475) • Per-Hop Behaviors (PHB, RFC2474, 2597, 2598)

24. Architecture • “Complex at edge, Simple at core.” • At edge: • Classifying • Metering • Marking • Conditioning • At core • BA classifying • Queuing and scheduling

25. Mechanisms • Diffserv Code Point (DSCP) • Behavior Aggregate (BA) • Per-Hop Behaviors (PHB) • Expedited Forwarding (EF, RFC3246) • Assured Forwarding (AF, RFC2597)

26. DSCP • Edge routers mark packets of different classes with different DSCP. • Core routers treat packets with different level of services according to its DSCP. • DS field: TOS(IPv4), Traffic class(IPv6) • CU: currently unused

27. Edge Functions • Meter monitors whether the incoming packet flow conforms to the negotiated traffic profile. • Shaper spaces the incoming packets to the negotiated traffic rate.

28. PHB • Per-Hop Behavior is a description of the externally observable forwarding treatment applied at a differentiated services-compliant node to a behavior aggregate. • EF is intended to provide a building block for low delay, low jitter and low loss services by ensuring that the EF aggregate is served at a certain configured rate. • The AF PHB group provides delivery of IP packets in four independently forwarded AF classes. Within each AF class, an IP packet can be assigned one of three different levels of drop precedence.

30. PHB Implementations • Priority queue • WFQ • RED with In and Out (RIO) • Weighted RED (WRED)

31. E2E DiffServ • DS Domain • Bandwidth Broker (BB) • Service Level Agreement (SLA)

32. Adjacent BB Adjacent BB Inter-Domain Interface Policy Manager Interface Application Server User/App Interface Network Management Interface User/Host Network Operator Data Repository Routing Information Intra-Domain Interface Edge Routers Edge Routers BB

33. ATM QoS Guarantees ? Network Architecture Internet ATM ATM ATM ATM Service Model best effort CBR VBR ABR UBR Congestion feedback no (inferred via loss) no congestion no congestion yes no Bandwidth none constant rate guaranteed rate guaranteed minimum none Loss no yes yes no no Order no yes yes yes yes Timing no yes yes no no

34. Service Classes

35. ABR • ABR Resource Management (RM) cells • Virtual Source/Virtual Destination

36. RSVP receiver generates reservation soft state (refresh/timeout) separate from route establishment QoS can change dynamically receiver heterogeneity ATM Q.2931 sender generates connection request hard state (explicit delete) concurrent with route establishment QoS is static for life of connection uniform QoS to all receivers RSVP v.s. Q.2931